It's hard to measure big waves at sea. No one's around to see them, and remote monitoring is difficult, because the waves can smash scientific instruments to bits.

But some science instruments sitting on the bottom of the sea 75 miles off the coast of Mississippi survived Hurricane Ivan last fall and lived to tell the tale -- of towering 90-foot-plus waves. These are perhaps the tallest, most extreme waves ever recorded with modern instruments.

The study, reported in the journal Science this week, says the biggest waves may have been as high as 130 feet. It suggests that big waves like these may be the norm for hurricanes rather than freak, rogue events.

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